Situation · DIY

Drafts, water or daylight under the garage door: which seal to fix

A closed door has several gaps and each takes a different seal. How to tell which one failed, what each costs, and where insulation fits.

What you’re seeing and hearing

Daylight under the closed door, leaves blown in after a windy week, or the heater running longer than it should. Source: The best garage door weather seal
Daylight at the corners but not the middle: the slab isn’t flat, and a new bottom seal alone won’t close that. Source: The best garage door weather seal
A draft along the sides or top with no visible gap: the jamb seal has stiffened in the sun while still looking fine. Source: The best garage door weather seal

Yes. A failed seal costs comfort and energy, not safety.

Air leaking at the bottom, sides and top bypasses the door’s insulation entirely: an R-18 door can lose most of its benefit to a failed bottom seal. Source: Garage door insulation R-value explained

Yours: three seals, each a weekend job.

Bottom U-seal: slides into the retainer along the bottom of the door. Match the retainer profile (T-style, bead or P-bulb). A 16-foot strip is $15 to $40. Source: The best garage door weather seal
Threshold seal: bonded to the floor, for a slab that has sloped or settled. It needs clean, dry concrete above freezing to cure. A 16-foot kit is $50 to $120. Source: The best garage door weather seal
Jamb weatherstripping: the flap on the sides and top of the opening, pressing lightly on the door. It needs a miter saw and galvanized finish nails; $40 to $80 for a single-car opening. Source: The best garage door weather seal
To test the jamb seal, run a lit incense stick along it on a windy day with the door closed. If the smoke pulls, the seal is gone. Source: The best garage door weather seal

A bottom seal lasts five to ten years before it loses its compression memory: it goes chalky, cracks, or stays flat and stops springing back. Source: The best garage door weather seal
The jamb seal lasts ten to fifteen years with moderate sun. Source: The best garage door weather seal
For an attached garage whose door is eight or ten years old, all three seals come to under $200 in materials. Source: The best garage door weather seal
Insulation is a separate question: a single-skin steel door is about R-0 and a polyurethane-injected one R-12 to R-18. For a detached, unconditioned garage, going past R-12 buys little. Source: Garage door insulation R-value explained

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Illustrative example

AI-generated illustrative homeowner, not a customer.